High resolution THz scanning for optimization of dielectric layer opening process on doped Si surfaces

Diffused IBC solar cells based on non-fire-through (NFT) metallization can achieve higher performance with respect to FT metallization, thanks to lower contact resistance. Less resistive contacts allows for lower metal fraction and thus lower contact recombination. For the application of NFT contacts, the rear side dielectric passivation layer needs to be locally opened. Standard processes for dielectric opening include laser ablation, use of etching pastes or masking and etching. In all this cases it is important that the opening process does not cause any damage to the diffusion below the contacts. We present a fast inspection method based on THz near-field scanning that allows investigating the diffusion layers after dielectric opening with spatial resolution suited for the small feature size of standard IBC solar cells. This method can be used to optimize crucial parameters of the dielectric opening without processing full cells. In this paper, we use THz scanning to optimize the curing temperature of the etch paste used to open the dielectric passivation layers on solar cells half-fabricates. After optimization, full cells are processed with top efficiency of 20.8%.